1. Field of the Invention
The present invention relates generally to a method for securing component parts together, and particularly to such a method that is especially useful for securing parts made of dissimilar materials.
2. Description of the Prior Art
The prior art is replete with disclosures of various methods and apparatus for securing component parts together, including parts made of dissimilar materials. For example, U.S. Pat. No. 3,367,809 to Soloff discloses a method for ultrasonically staking thermoplastic parts to other parts. For another example, U.S. Pat. No. 3,483,611 to Balamuth et al. discloses methods and apparatus for ultrasonically staking and riveting component parts together. Also, U.S. Pat. No. 4,106,962 to Adams et al. discloses a method for ultrasonically securing metallic and thermoplastic parts together, wherein ultrasonic energy is applied to an apertured depression in the metallic part while the depression is pressed against the thermoplastic part, causing an adjacent portion of the thermoplastic part to soften, flow through the aperture, fill the depression therearound, and thereby lock the two parts together upon cooling.
FIG. 1 of the drawings herein illustrates a process, known in the prior art as conventional ultrasonic staking, which fuses parts together by using heat generated from contact together with mechanical pressure and high-frequency sound waves. To use ultrasonic staking effectively, it is necessary that one of the parts, such as substrate 1, be made of a material that responds to ultrasonic heating. The stake 2 is a raised feature on substrate 1. Hole 3 is provided in mating part 4 to fit over stake 2. After mating part 4 is properly aligned with substrate 1, stake 2 is heated by means of an ultrasonic horn 5. As stake 2 melts, pressure is maintained thereon. That presses the stake down, so that it becomes larger than hole 3. Horn 5 is then removed, leaving the two parts 1 and 4 held together in a manner that is similar to conventional riveting.
There are two disadvantages in using ultrasonic staking in an automated process: (1) ultrasonic-horn-to-stake alignment is critical, in that any misalignment adversely affects the integrity of the bond; and (2) any design changes require either retrofitting the old parts or fabricating new ones.
Conventional riveting is an alternative method for fastening parts together. This method also has disadvantages when used in an automated process. Holes are necessary in both parts being joined. A rivet must be placed in those holes and forced down, holding the parts together mechanically. Properly aligning the holes and properly orienting the rivet make conventional riveting difficult to automate.